Process of producing metallic articles substantially free from impurities



Patented Mar. 14, 1939 UNITED STATES PROCESS OF PRODUCING METALLIC ARTI-CLES SUBSTANTIALLY FREE FROM IM- PURITIES John Tyssowski, Dobbs Ferry,N. Y.

- No Drawing. Application April 28, 1937,

Serial No. 139,503

2 Claims.

This application is a continuation in part of my copending application,Serial No. 68,689, filed March 13, 1936.

The invention relates to the art of refining metal and plasticallyconverting it into articles that are substantially free from impurities.

The principal object of the invention is to improve the process ofproducing so-called brittle cathodes and subsequently coalescing themand plastically transforming them, as by extrusion, into merchantableshapes without melting the metal.

The invention is particularly applicable to the refining of copper, andthe plastic transformation of it into substantially pure articles, andthe invention will be described in its application to that I metal.

The various steps of the process upon which this invention is animprovement are disclosed in the patent to Stout No. 1,822,939 and thepatents to Stout and Osborn Nos. 1,846,697 and 1,938,608. Briefly thesteps are as follows:

1) The electrolytic production of a metal cathode having specialcharacteristics which distinguish it from the tough, dense cathodes madeby the usual electrolytic process and which are intended for subsequentmelting prior to further treatment. The special characteristics of thecathode are its coarse crystalline structure, its porosity, itsbrittleness, it frangibility, its ability to be readily stripped fromthe starting blank or starting cathode, and its very rough and raggedexterior surface. Cathodes having these special characteristics arecalled brittle cathodes and are produced by coating a suitable blank,used as the starting cathode in the electrolytic cell, with asphalt, orthe like, having the requisite prop-' order to increase their life it iscustomary to treat the moulds with a mould wash before each castingoperation. The mould wash also prevents sticking of the castings in themoulds and thereby facilitates their removal. In casting copper anodesthe mould wash usually employed comprises an emulsion of silica orsilicates.

(2) Stripping the deposited brittle cathode from the starting blank,breaking it into small pieces, and compressing the pieces into billets,

(3) Subjecting the billets to a fluid cleansing treatment at an elevatedtemperature below the melting point of the metal. The cleansing fluidpenetrates the interstices of the billet and substantially reduces suchimpurities as sulfur from any sulfate entrained from the electrolyticbath,

oxygen which may be present in the sulfates and oxygen which may be dueto oxidation of the metal from exposure to the air, carbonaceousmaterial from the coating compound used on the starting cathode, arsenicand antimony from any electrolyte that might adhere to the brittle oathsode when it is removed from the electrolytic cell, and perhaps otherimpurities. This cleansing process is supposed to leave all surfaces ofthe metal particles clean and pure so that the particles will properlycoalesce in the subsequent step.

(4) subjecting the cleansed billets to pressure to coalesce them andextrude the billets in the form of bars, rods, etc. The coalescence andextrusion of the metal is effected at an elevated temperature below themelting point of the metal. The metal is maintained in a neutral ornoninjurious atmosphere from the time it is cleansed of its impuritiesto the time the metal has been extruded. The extrusion of the billetunder pressure coalesces the metal particles into a homogeneous mass andcauses new crystal grain growth throughout the mass.

In practicing the complete coalescence process outlined above, in theproduction of extruded copper articles it was found that while thecleansing step (step No. 3 above) was intended to remove allobjectionable impurities, there were certain substances in the form ofdiscrete particles that resisted removal by the treatment and foundtheir way into the extruded articles. Their presence in the extrudedarticles was highly objectionable especially when the extruded articleswere further fabricated into articles of small cross section,particularly fine wire. I discovered that these substances wereparticles of silica or silicates and I traced them to the silica orsilicates contained in the anode mould wash. I found that when the anodecastings were removed from the moulds, some of the mould washunavoidably adhered to the surfaces of the castings. During thesubsequent dissolution of the anode in the electrolyte, the adheringmould wash particles were released, and while most of them settled tothe bottom of the tank where they could be removed along with othersediment beforethe next charge of anodes was placed in the tank, some ofthem found their way over to the cathodes and became attached to them asan impurity. The

rough surface of the brittle cathode, and the numerous pores throughoutits mass, afforded abundant lodgment" places for the silica and silicateparticles, thus making the brittle cathode more subject to contaminationby these impurities than would be the case with the usual dense cathodehaving a relatively smooth surface. Inasmuch as the brittle cathodes areconverted by the coalescence process directly into extruded articleswithout melting, no opportunity was afforded for slagging off the silicaor silicate particles.

Having thus ascertained the nature-and cause of the objectionablediscrete particles in the extruded articles I thereupon improved thecomplete coalescence process outlined above for refining and plasticallytransforming copper and other metals into merchantable articles, byeliminating, or materially reducing, the possibility of the mould washparticles finding their way into the end products.

In accordance with my invention, substantially all mould Wash particleswhich happen to adhere to the anodes are prevented from reaching thebrittle cathodes, thus keeping them out of the coalesced finishedarticles.

I accomplish this by the use of a mould wash for the anode moulds whichis chosen not only from the standpoint of its ability to perform itsusual functions of protecting the moulds and facilitating removal of thecastings, but also with due regard to how any particles of the mouldwash which adhere to the anodes are going to behave in the subsequentformation of the brittle cathodes in the electrolytic refining step. Themould wash, to be satisfactory for my purpose, should not only fulfillits usual purposes but it should also be capable of dissolving in theelectrolyte used in the refining step, and it should not form insolublecompounds with the electrolyte. Substantially all of the mould washparticles adhering to the anodes will then be dissolved in theelectrolyte during the refining step and will remain in solution andfew, if any, will reach the cathodes to contaminate them. The mould washshould have a melting point above the temperature of the molten metalbeing cast in the mould and it should not form compounds or liquidsolution with the molten metal being cast. Nor should it form compoundswith the metal of the mould or otherwise detrimentally affect it. I havefound that zinc oxide answers all of these requirements.

The moulds in which the copper anodes are cast may be of any appropriatemetal but they are preferably made of refined copper. Unless the mouldsare treated with a mould wash there would be a slight but accumulativecorrosive and erosive action on the surface of the copper moulds due tothe impingement of, and contact with, the molten copper being cast. Toprolong their life, and to facilitate removal of the cast anodes fromthe moulds, the copper moulds are cooled by any suitable means betweencasts and the surface of each mould is treated before the next cast witha zinc oxide mould wash. The zinc oxide may be mixed with a suitableliquid, preferably water, and may be applied in the usual way as byspraying or brushing it on the surface of the mould. The copper to berefined, and converted into a brittle cathode, is cast into anodes inthe moulds thus treated, and then the cast anodes are removed from themoulds and assembled in the electrolytic tank with the starting blanksor starting cathodes. The electrolyte may be a dilute solution ofsulfuric acid. The refining operation is now started by passing anelectric current through the electrolytic cell. Any mould wash particleswhich adhere to the copper anodes when they are removed from theirmoulds are dissolved in the electrolyte, at least to a substantialextent and remain in solution and very few, if any, of them ever reachthe brittle cathodes to contaminate them. At the end of the refiningoperation, and before the next charge of anodes is placed in theelectrolytic tank, any sediment in the bottom of the tank may be removedin the usual manner, together with any mould wash particles which maynot have been dissolved and which have settled to the bottom of thetank.

The dissolving of the mould wash particles in the electrolyte beforethey have a chance to be caught by the numerous ledges and intersticesof the rough brittle cathode, and their continuance in solution,prevents the cathode from being contaminated by them, or'by insolublecompounds formed from them, and the extruded articles will therefore bepractically free from contamination either by particles of the mouldwash, or particles of insoluble compounds. If the cathodes were of theusual tough dense type, and subsequently melted for further treatment,an opportunity would be afforded for slagging off in the melting furnaceany insoluble mould wash particles that happen to reach the cathode andconsequently would not appear in the cast articles to any large extent.However, in the process of making brittle cathodes. and converting themdirectly into articles by coalescence and extrusion no such opportunityis afforded as the metal is not melted at any stage of the process. Itis, therefore, important in that type of process to provide for theelimination of the mould wash particles in some other way.

It will now be seen that my invention makes it possible to producesubstantially pure brittle cathodes so far as contamination by mouldwash particles is concerned. The other impurities are satisfactorilyremoved by the cleansing step which precedes the coalescence, andtherefore the elimination of both sets of impurities makes it possibleto produce substantially pure end products containing no mould Washparticles which, as above stated, are particularly objectionable wherethe brittle cathodes are coalesced and extruded into bars, rods or anyshapes subsequently tobe fabricated into articles of small crosssection, particularly into fine wire.

I claim:

1. A process of producing a metallic article which comprises treating a'mould with a zinc oxide mould wash, casting the metal from which L thearticle is to be formed into anode form in said treated mould,electrolytically producing a refined brittle cathode from the anode, andcoalescing the brittle cathode and transforming it without melting intoa merchantable shape by pressure, whereby the final article issubstantially uncontaminated by impurities from the casting operation.

2. A process of producing a copper article which comp-rises treating acopper mould with a zinc oxide mould wash, casting copper from which thearticle is to be formed into anode form in said treated mould,electrolytically producing a refined brittle cathode from the anode, andcoalescing the brittle cathode and transforming it without melting intoa .merchantable shape by pressure, whereby the final article is substantially uncontaminated by impurities from the casting operation.

JOHN TYSSOWSKI.

